Magnetic Effect of Electric Current
Ampere's Circuital Law Ampere's Circuital Law states that the line integral of Magnetic Induction is equal to the product of absolute permeability and Current flowing through the coil . Magnetic Lines of Force are also referred to Amperian Loops . ∫ B.dl = μ0 I Straight Conductor B = μ0 I / 2πa Solenoid B = μ0 NI Torroid B = μ0 NI Galvanometer A Galvanometer is used to measure a small current . Thus, a Galvanometer is mostly used to only detect the presence of current . To measure larger values of current , a galvanometer is converted to an Ammeter by connecting a Shunt resistance of low resistance in parallel to the galvanometer . A Voltmeter can be prepared from a galvanometer by adding a resistor of infinitely high resistance in series to the galvanometer . Moving Coil Galvanometer A moving Coil Galvanometer consists of a soft iron core of high permeability , on which a rectangular coil is wound . The coil is then placed between the poles of a strong magnet . The coil rotates with a change in Current ... i α θ Suspended The coil is suspended from a rigid support . On the suspension cable , there is a mirror . Light is made to fall on the mirror . When the deflection begins , the reflected ray moves along a calibrated scale . This measures the current . Pivoted The coil is pivoted from both ends . The top end of the coil is connected to a pointer , which moves with deflection in the coil . The pointer is then pointed on a semi-circular scale . The pivoted set-up is easier to handle than the suspended set-up . Ammeter To measure larger values of current , a galvanometer is converted to an Ammeter by connecting a Shunt resistance of low resistance in parallel to the galvanometer . The maximum current measured by galvanometer is called as Galvanometer Current (ig) or Full scale deflection . When shunt is connected , only a fraction of current flows through the galvanometer . For e.g. consider a Galvanometer of Full Scale Deflection 10 mA . Suppose the range of Ammeter is increased to 100 mA . Now if 50 mA Current is flowing through the Ammeter , 5 mA will flow through Galvanometer and 95 mA will flow through Shunt . Thus , the galvanometer reading will be 5 . But , since 10 mA was increased to 100 mA (10 times ) the least count also changes . Now , the least count is 10 mA as opposed to 1 mA initially . Thus the reading is 5 and the value of Current measured is 50 mA . The shunt resistance should be of lower resistance , so that most current flows through the shunt . The Shunt resistance should be decreased to increase the range of an Ammeter . Voltmeter A Voltmeter can be prepared from a galvanometer by adding a resistor of infinitely high resistance in series to the galvanometer . The added resistance provides a huge potential drop , which is required to measure the potential difference . To increase the range of voltmeter , the resistance should be increased . Cyclotron Cyclotron is an instrument used to accelerate a positively charged particle . The cyclotron consists of two hollow semi-cylindrical metal boxes . These are called as 'dees' . There s a gap between the dees . The dees are kept under a strong magnetic field . A potential of the order 106 V is applied between the dees and high frequency of 107 Hz . The particle is kept in the gap . Due to high frequency of Alternating voltage , the dees keep switchng their polarities . If D1 is at negative potential at first , the charged particle moves away from D2 . This force acting on the charge due to magnetic field provides necessary centripetal force . This force helps the charge to be accelerated and moves towards the gap between the dees . r = mv/ qB t = 2mπ / qB = 2πr / v f = 1/t = qB / 2πm vmax = qBR / m 'K.E. = q2B2R2 / 2m ' Category:Physics